Growing environmental awareness has led to recent improvement in legal systems for controlling the fuel volatilization. Especially in the automotive industry, the fuel volatilization control is seriously demanded particularly in the United States. This demand has raised needs for materials having excellent fuel-barrier properties.
Fuel delivery hoses used are laminated hoses (made of rubber except for a barrier layer) including a barrier layer formed of a fluororesin for lowering the fuel permeability. Recent strong demands for reducing environmental loads have raised needs for lower fuel permeability of the barrier layer. Trials have been made for ensuring lower permeability by increasing the thickness of the barrier layer or using perhalogen fluororesins that has the lowest permeability among fluororesins. Increase in the thickness of the barrier layer (fluororesin) however increases the weight of the resulting hose, leading to a disadvantage from the standpoint of energy conservation. Further, such a hose has poor bendability (flexibility), which is disadvantageous in terms of handleability (assembling property).
In the case where a perhalogen fluororesin is used for a barrier layer, such a barrier layer is not easily adhered to rubber of inner and outer layers. To improve the adhesiveness, a surface treatment on the resin or a treatment of wrapping the layer with a film or tape is needed. As a result, the procedure is complicated to cause practical disadvantages such as significant reduction in productivity and great increase in the cost.
As disclosed in Patent Literature 1, for example, a known means for enhancing the adhesion between a fluororesin layer and a rubber layer is use of epoxidized rubber or a mixture of epoxidized rubber and another rubber for a rubber layer. Moreover, as disclosed in Patent Literature 2, for direct adhesion of a rubber to a fluororesin, a thermoplastic fluororesin having a reactive functional group such as a carbonyl group is used as a fluororesin, and a polyfunctional compound such as triallyl isocyanurate is added to at least one of the thermoplastic fluororesin and a rubber layer.
As disclosed in Patent Literature 3, also known is a fuel hose having a layered structure in which a diene rubber layer and a vinylidene fluoride copolymer (THV) layer are adjacent to each other, the diene rubber layer formed of a diene rubber, such as NBR, blended with a sulfur vulcanizing agent, at least one of a metal calbamate and a thiazole metal salt, and magnesium oxide, together with a DBU salt and the like.
As disclosed in Patent Literatures 4 and 5, the adhesiveness of a curable elastomeric compound to a fluoropolymer layer is known to be enhanced by using fluoropolymers including at least one monomer containing plural hydrogen atoms or fluoropolymers essentially including vinylidene fluoride, with a dehydrofluorinated composition mixed therein.
Patent Literature 6 discloses a laminate including a rubber layer (A), a fluororesin layer (B) on the rubber layer (A), wherein the rubber layer (A) is a layer formed of a rubber composition for vulcanization, the rubber composition for vulcanization containing an unvulcanized rubber (a1), at least one compound (a2) selected from the group consisting of 1,8-diazabicyclo(5.4.0)undec-7-ene, 1,5-diazabicyclo(4.3.0)-non-5-ene salts, 1,8-diazabicyclo(5.4.0)undec-7-ene, and 1,5-diazabicyclo(4.3.0)-non-5-ene, magnesium oxide (a3), and silica (a4), the compound (a2) being contained in an amount of more than 1.0 part by mass but not more than 5.0 parts by mass based on 100 parts by mass of the unvulcanized rubber (a1), the fluororesin layer (B) being a layer formed of a fluoropolymer composition, the fluoropolymer composition containing a fluoropolymer (b1) having a copolymer unit derived from chlorotrifluoroethylene.